A cell sheet cultured in a container is anchored to the surface of the container, and the cell sheet may be released from the surface of the container using a protease such as Dispase (registered trademark) in order to recover this cell sheet. In such a releasing procedure using a protease, not only may the cells be damaged, but also the extracellular matrix produced during the culture may also be decomposed. Furthermore, since most proteases are materials derived from animals, the application of such proteases to a cell sheet for regenerative medicine is problematic in terms of safety. In view of this point, for example, JP-A 6-104061 proposes a method of releasing cultured cells anchored to the surface of a container without using a protease to recover the cells. More specifically, a Petri dish whose surface is covered with poly(N-isopropylacrylamide) is prepared, and bovine aortic endothelial cells are cultured at 37° C. on the Petri dish. The Petri dish is then cooled to 4° C. to change the surface of the Petri dish from hydrophobic to hydrophilic, thereby releasing and recovering the cultured cells.